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Variational approximations for correlation functions in quantum field theories

Cécile Martin
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Abstract

Applying the time-dependent variational principle of Balian and Vénéroni, we derive variational approximations for multi-time correlation functions in $Φ^4$ field theory. We assume first that the initial state is given and characterized by a density operator equal to a Gaussian density matrix. Then, we study the more realistic situation where only a few expectation values are given at the initial time and we perform an optimization with respect to the initial state. We calculate explicitly the two-time correlation functions with two and four field operators at equilibrium in the symmetric phase.

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Cécile Martin. 1999-09-29. Variational approximations for correlation functions in quantum field theories. https://doi.org/10.1006/aphy.1999.5978

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